Search

We show that an individual droplet of liquid metal can be a source of coherent terahertz radiation when it is excited by two femtosecond laser pulses of the same frequency. Under certain delays between these pulses, the intensity of terahertz radiation increases by more than 3 orders of magnitude. We describe the experimental results with the model of dynamic gain control, which considers the interaction of both laser pulses with the droplet and explains the terahertz-generation process by taking into account the dynamics of electrons and ions after photoionization of the metal droplet. The spatial distribution of terahertz radiation has a forward-directed contribution, whose polarization properties are well described by a nonlinear susceptibility of the second order. Our theoretical estimations based on the experimental data show that under the dynamic gain control the observed terahertz output can be considerably increased. Joint generation of x-ray, ultraviolet, and, as shown in the present work, terahertz radiation allows one to forecast that a free-falling photoexcited droplet of liquid metal is a promising source of multifrequency electromagnetic radiation for extreme nonlinear laser science.

In this paper, we propose a switchable focuser device based on a Fresnel zone plate (FZP) structure for terahertz (THz) applications. Each FZP contains seven rings, etched in thin VO2 film with the designed focal lengths of 50 and 100 mm for 3.7-THz frequency. Temperature-induced VO2 phase transition leads to the change in dielectric susceptibility of the material, which allows one to switch on and off the focusing properties of the device. The devices were tested with radiation of 3.1 and 3.7 THz emitted by quantum cascade lasers. Experimental results were compared with numerical simulations. In this article, we compare the FZP based on VO2 films with different properties and show that a thicker VO2 film reveals higher focusing efficiency, while a thinner one reveals a higher modulation ratio for the peak intensity at the focal point of FZP. We demonstrate experimentally the near-diffraction-limited size of the beam in the focal point of the device. Switching between two phase states of the VO2 films results in up to the 38-fold change of intensity in the focal point.

In this work we experimentally and theoretically investigate the mutual action of three copropagating waves in isotropic nonlinear medium (liquid nitrogen). Two waves are the first and the second harmonic of the Ti:Sa laser system, and the third one is the terahertz wave generated in the spark of optical breakdown of air. After propagation through liquid nitrogen the change in terahertz polarization state is observed. We attribute this phenomenon to the nonlinear “Terhune-like” mutual rotation of the main axis of a polarization ellipse of terahertz radiation.

In this work, we the study the possibility of controlling the temperature of ultrafast light induced insulator-metal phase transition in VO 2 films by photosensibilization with thin layer of organic dyes which can directly inject photoelectrons into the VO 2 film triggering a photoelectron-assisted phase transition.

In this work we investigate and compare the features of the THz generation process caused by an optical breakdown of air both in a “filament” and “micro-plasma” regimes. We explore efficiency, a spatial and spectral distributions of terahertz radiation in each case.

Measurement of the absolute value of the humidity of the cornea of the human eye and its dynamics is of paramount importance for the preservation of eyesight. In the present paper we have demonstrated that terahertz technologies can be practically applied for quantitative measurement of the physiological dynamics of tear film and sensing of corneal tissue hydration. We suggest uses of the equipment for application in clinics and a method for absolute calibration of the values for measurement. The proposed method is fundamentally different from existing and currently available methods of ophthalmological diagnosis. This suggests that the developed technique may have high diagnostic significance and can be used in the study and treatment of several diseases of the ocular surface.